Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image of a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design according to an embodiment; and,

FIG. 2 is the second image thereof.

The subject matter in this patent includes a process or period in which an image changes into another image. This process or period forms no part of the claimed design.

The broken lines showing the display screen or portion thereof with transitional graphical user interface are for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or a portion thereof with transitional graphical user interface, as shown and described. 